Tape-thickness measuring method, and tape-running control method using the tape-thickness measuring method

ABSTRACT

A tape running control method in which a tape runs between a supply reel and a take-up reel, and a rotation speed of said take-up reel is controlled by using rotation periods of said supply reel and said take-up reel, whereby a running speed of said tape is controlled. The method comprises the steps of detecting a thickness of said tape; calculating a predetermined total tape wound amount by using the detected thickness of said tape; and controlling the rotation speed of said take-up reel by using the thus-calculated total tape wound amount.

This application is a division of U.S. Ser. No. 09/211,359 filed Dec.14, 1998, now U.S. Pat. No. 6,079,653 which U.S. application is herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tape-thickness measuring method, anda tape-running control method using the tape-thickness measuring method.In particular, the present invention relates to a tape-thicknessmeasuring method in which a belt-type recording medium is caused to runat a fixed speed, and a tape-running control method using thetape-thickness measuring method.

2. Description of the Related Art

A DDS (Digital Data Storage) has been developed as a large-capacity databacking-up device. In the DDS, backup data is recorded in a recordingformat of a DAT (Digital Audio Tape-recorder). In the DAT, a magnetictape is caused to run at a fixed speed, data is recorded on the magnetictape, and, also, data is reproduced from the magnetic tape. A belt-typerecording medium such as a magnetic tape has a capacity larger than thatof a disk-type recording medium. Therefore, when a large amount of datashould be backed up, the DDS is useful.

FIG. 1 shows a general arrangement of one example of DDS in the relatedart.

In the DDS in the related art, when data is recorded or reproduced, amagnetic tape 3 contained in a DAT tape cassette 2 is drawn out from asupply reel 4, is caused to run through supply poles 5 and a guideroller 6, and is wound on a rotation drum 7 through a predeterminedangle. Then, the magnetic tape 3 is caused to run through take-up poles8 and a guide roller 9, and is drawn into a take-up reel 10 of the DATtape cassette 2.

At this time, the magnetic tape 3 is sandwiched by a capstan shaft 11 arotated by a capstan motor 11 and a pinch roller 12 on the side of thetake-up reel 10, and is caused to run at a fixed speed as a result ofbeing driven by the rotating capstan shaft 11 a.

At this time, the running speed of the magnetic tape 2 is determined bythe rotation speed of the capstan shaft 11 a, that is, the rotationspeed of the capstan motor 11. Therefore, in order to make the runningspeed of the magnetic tape 2 be fixed, the rotation speed of the capstanmotor 11 is maintained to be fixed.

For this purpose, an FG (Frequency Generator) 13 is attached to thecapstan motor 11, the rotation of the capstan motor 11 is detectedthrough the FG 13, and the rotation speed of the capstan motor 11 isfixed by servo control. Thereby, the running speed of the magnetic tape2 is maintained to be fixed.

However, in the DDS system 1 in the related art shown in FIG. 1, therunning speed of the magnetic tape is maintained to be fixed as a resultof servo control being performed on the capstan motor 11. In such asystem, it is necessary that the magnetic tape 3 be sandwiched by thecapstan shaft 11 a and the pinch roller 12. Therefore, because the tapethickness is reduced as high-density data storage is achieved, the tapemay be damaged.

A magnetic recording and reproducing apparatus in a capstan-less systemhas been proposed, in which apparatus the take-up reel is rotated by areel motor, and, as a result of rotating the take-up reel so that therunning speed of the magnetic tape is fixed, the capstan motor isomitted.

As such a magnetic recording and reproducing apparatus in thecapstan-less system, a magnetic recording and reproducing apparatus isdisclosed by Japanese Laid-Open Patent Application No. 9-500477, forexample.

In the magnetic recording and reproducing apparatus disclosed inJapanese Laid-Open Patent Application No. 9-500477, in accordance withservo information previously written in a magnetic tape, the rotation ofa take-up reel is controlled by a reel motor so that the running speedof the magnetic tape is fixed. In the magnetic recording and reproducingapparatus disclosed in Japanese Laid-Open Patent Application No.9-500477, it is necessary to write special servo information on themagnetic tape. Therefore, it is not possible to reproduce data from amagnetic tape on which such special servo information is not recorded.

Therefore, a magnetic recording and reproducing apparatus has beenproposed in which the running speed of a magnetic tape is detected byusing an encoder, and the rotation speed of a take-up reel is controlledby a reel motor by using the thus-detected tape running speed.

FIG. 2 shows a block diagram of another example of a magnetic recordingand reproducing apparatus in the related art. In the FIG., the samereference numerals are given to the parts the same as those shown inFIG. 1, and descriptions thereof will be omitted.

In the magnetic recording and reproducing apparatus 100, an encoder 101is provided instead of a capstan shaft. The running speed of themagnetic tape 3 is detected in accordance with the rotation of theencoder 101. A detection signal produced by the encoder 101 is providedto a control circuit 102.

The control circuit 102 controls the rotation speed of a reel motor 103,which rotates a take-up reel 10, by using the detection signal.

The take-up reel 10 is.driven by the reel motor 103 and fixes the speedat which the magnetic tape 3 is taken up by the take-up reel 10, thusmaintaining the running speed of the magnetic tape 3 to be fixed.

In a magnetic recording and reproducing apparatus in which a taperunning speed is detected by an encoder or the like, and rotation of atake-up reel is controlled by a reel motor by using the detected runningspeed of a magnetic tape, it is necessary to provide an encoder or thelike instead of a capstan motor. Thereby, miniaturization of themagnetic recording and reproducing apparatus cannot be achieved, and,also, because the encoder is expensive, cost reduction of the magneticrecording and reproducing apparatus cannot be achieved.

Further, an encoder shaft, which is rotated by the magnetic tape androtates the encoder, is in contact with the magnetic tape, and isrotated by using a friction force. Thus, the encoder detects the runningspeed of the magnetic tape. Therefore, when the magnetic tape slides onthe encoder shaft, an error occurs between the actual running speed ofthe magnetic tape and the detection signal of the encoder. Thereby, itis not possible to precisely control the running speed of the magnetictape.

Therefore, the applicant of the present application proposed, inJapanese Patent Application No. 9-262430, a tape running method, inwhich tape running is controlled only by using the rotation periods of asupply reel and a take-up reel.

In the magnetic recording and reproducing apparatus in the related artin which the running speed of the magnetic tape is fixed by the capstanmotor, because it is necessary to provide the capstan motor, pinchroller and so forth, miniaturization and cost reduction cannot beachieved. Further, the magnetic tape, the thickness of which is reduced,may be damaged.

In the magnetic recording and reproducing apparatus disclosed inJapanese Laid-Open Patent Application No. 9-500477, the rotation of thetake-up reel is controlled by the reel motor, so that the running speedof the magnetic tape is fixed, by using the servo information previouslywritten on the magnetic tape. Therefore, recording or reproducing cannotbe performed on the magnetic tape on which the servo information has notbeen written.

In the magnetic recording and reproducing apparatus in which the runningspeed of the magnetic tape is detected through the encoder-or the like,and the rotation of the take-up reel is controlled by the reel motor byusing the detected tape running speed, because it is necessary toprovide the encoder or the like instead of a capstan motor,miniaturization of the apparatus cannot be achieved, and, also, becausethe encoder is very expensive, cost reduction of the apparatus cannot beachieved.

Further, the encoder shaft, which is rotated by the magnetic tape androtates the encoder, is in contact with the magnetic tape, and isrotated by using a friction force. Thus, the encoder detects the runningspeed of the magnetic tape. Therefore, when the magnetic tape slides onthe encoder shaft, an error occurs between the actual running speed ofthe magnetic tape and the detection signal of the encoder. Thereby, itis not possible to precisely control the running speed of the magnetictape.

In the magnetic recording and reproducing apparatus proposed by theapplicant of the present application in the Japanese Patent ApplicationNo. 9-262430, because the running speed of the magnetic tape iscontrolled only by using the rotation periods of the supply reel and thetake-up reel, when a system in which the tape is taken up 1000 through2000 turns is considered, the maximum diameters of reels vary due tovariation in the tape thickness. When the maximum diameters of reelsvary, variation in the rotation periods of the supply reel and thetake-up reel occur. As a result, the tape running speed varies, and,thereby, the tape running cannot be controlled precisely.

SUMMARY OF THE INVENTION

The present invention is directed to eliminating the above-mentionedproblems. An object of the present invention is to provide atape-thickness measuring method by which the tape thickness can beeasily measured from the rotation periods of reels and the tape runningcan be controlled precisely, and a tape-running control method using thetape-thickness measuring method.

A tape-thickness measuring method, according to the present invention,used in a tape running apparatus in which a tape runs between a supplyreel and a take-up reel, comprises the steps of:

detecting rotation periods of the supply reel and the take-up reel whenthe take-up reel has rotated predetermined numbers of revolutions;

calculating a number of turns of the tape remaining on the supply reelby using the thus-detected rotation periods; and

calculating a thickness of the tape by using the thus-calculated numberof turns of the tape remaining on the supply reel.

The tape-thickness measuring method may comprise the steps of:

calculating a ratio between the rotation periods of the supply reel andthe take-up reel detected when the take-up reel has rotated apredetermined first number of revolutions;

calculating a ratio between the rotation periods of the supply reel andthe take-up reel detected when the take-up reel has rotated apredetermined second number of revolutions;

obtaining a difference between a number of revolutions which the supplyreel has rotated when the take-up reel has rotated the predeterminedfirst number of revolutions and a number of revolutions which the supplyreel has rotated when the take-up reel has rotated the predeterminedsecond number of revolutions;

calculating the number of turns of the tape remaining on the supply reelby using the thus-calculated ratios between the rotation periods and thethus-obtained difference; and

calculating the thickness of the tape by using the thus-calculatednumber of turns of the tape remaining on the supply reel.

Specifically, the thickness of the tape is calculated as follows:

The diameter (mm) of a supply-reel hub and a take-up-reel hub isrepresented by ‘d,’ the thickness (mm) of the tape is represented by‘t,’ the running speed (mm/sec) of the tape is represented by ‘V,’ thenumber of turns of the tape wound on the supply reel hub is representedby Ns, the number of turns of the tape wound on the take-up reel hub isrepresented by Nt, the diameter (mm) of the tape-wound supply-reel hubis represented by øs and the diameter (mm) of the tape-woundtake-up-reel hub is represented by øt.

Then, the diameter øs of the tape-wound supply-reel hub can be expressedas follows:

øs=d+2·Ns·t (mm)  (1)

The diameter øt of the tape-wound take-up-reel hub can be expressed asfollows:

øt=d+2·Nt·t (mm)  (2)

The rotation period Ts of the supply reel and the rotation period Tt ofthe take-up reel can be expressed as follows:

Ts=(øs·π)/V (sec)  (3)

Tt=(øt·π)/V (sec)  (4)

From the above equations (1) through (4), the ratio between the rotationperiods Ts, Tt of the supply reel and the take-up reel can be expressedas follows:

Ts/Tt=øs/øt=(d+2·Ns·t)/(d+2·Nt·t)  (5)

From the above equation (5), the thickness ‘t’ of the tape can beexpressed as follows:

t=(d/2)·(k−1)/(Ns−k−Nt)  (6)

In the above equation, k=Ts/Tt.

In the above equation, although the number Nt of turns of the tape woundon the take-up-reel hub can be obtained as result of the number ofrevolutions which the take-up reel has rotated being counted since thetape started being wound on the take-up-reel hub, the number Ns of turnsof the tape remaining on the supply-reel hub is the unknown.

When the take-up reel has rotated a predetermined number ‘A’ ofrevolutions since the tape started being wound on the take-up reel hub,the equation (6) is expressed as follows:

t=(d/2)·(ka−1)/(Nsa−ka·A)  (7)

In the above equation, Nsa represents the number of turns of the taperemaining on the supply-reel hub, and ka represents the ratio betweenthe rotation periods of the supply reel and the take-up reel, at thistime.

Then, when the take-up reel has rotated a predetermined number ‘x’ ofrevolutions after rotating the predetermined number ‘A’ of revolutions,and, thereby, the number ‘z’ of turns of the tape has been reduced fromthe supply-reel hub, the number of turns of the tape remaining on thesupply-reel is (Nsa−z), and the equation (6) can be expressed asfollows:

t=(d/2)−(kax−1)/{(Nsa−z)−kax·(A+x)}  (8)

In the above equation, kax represents the ratio between the rotationperiods of the supply reel and the take-up reel at this time.

From the equations (7) and (8),

(d/2)·(ka−1)/(Nsa−ka−A)=(d/2)·(kax−1)/{(Nsa−z)−kax·(A+x)}  (9)

From the equation (9), the number Nsa of turns of the tape remaining onthe supply-reel hub can be obtained as follows:

Nsa={ka·(A+z+x·kax)−kax·(A+x)−z}/(ka−kax)  (10)

The number Nsa of turns of the tape remaining on the supply-reel hub,which was the unknown, can be obtained by the equation (10). As a resultof substituting the thus-obtained number Nsa in the equation (7), thethickness ‘t’ of the tape can be obtained.

Thus, from the rotation periods of the supply reel and the take-up reel,the thickness ‘t’ of the tape can be obtained. As a result, withoutusing special means, the measurement of the thickness of the tape can beperformed easily each time when a tape cassette is loaded.

A tape running control method, according to the present invention, inwhich a tape runs between a supply reel and a take-up reel, and arotation speed of the take-up reel is controlled by using rotationperiods of the supply reel and the take-up reel, and, thereby, a runningspeed of the tape is controlled, comprises the steps of:

detecting a thickness of the tape;

calculating a predetermined total tape wound amount by using thedetected thickness of the tape; and

controlling the rotation speed of the take-up reel by using thethus-calculated total tape wound amount.

In this method, because the predetermined total tape wound amount iscalculated by using the thickness of the tape, and, then, the rotationspeed of the take-up reel is controlled by using the thus-calculatedtotal tape wound amount, the rotation speed of the take-up reel can becontrolled in response to variation in the thickness of the tape.Therefore, precise control of the running speed of the tape can beperformed irrespective of the thickness of the tape.

The step of detecting the thickness of the tape may comprise the stepsof:

detecting rotation periods of the supply reel and the take-up reel whenthe take-up reel has rotated predetermined numbers of revolutions;

calculating a number of turns of the tape remaining on the supply reelby using the thus-detected rotation periods; and

calculating the thickness of the tape by using the thus-calculatednumber of turns of the tape remaining on the supply reel.

Further, the step of detecting the thickness of the tape may comprisethe steps of:

calculating a ratio between the rotation periods of the supply reel andthe take-up reel detected when the take-up reel has rotated apredetermined first number of revolutions;

calculating a ratio between the rotation periods of the supply reel andthe take-up reel detected when the take-up reel has rotated apredetermined second number of revolutions;

obtaining a difference between a number of revolutions which the supplyreel has rotated when the take-up.reel has rotated the predeterminedfirst number of revolutions and a number of revolutions which the supplyreel has rotated when the take-up reel has rotated the predeterminedsecond number of revolutions;

calculating the number of turns of the tape remaining on the supply reelby using the thus-calculated ratios between the rotation periods and thethus-obtained difference; and

calculating the thickness of the tape using the thus-calculated thenumber of turns of the tape remaining on the supply reel.

In this method, it is possible to obtain the thickness of the tape fromthe rotation periods of the supply reel and the take-up reel. As aresult, without using special means, the measurement of the thickness ofthe tape can be performed easily each time when a tape cassette isloaded. As a result, precise control of the running speed of the tapecan be performed.

Other objects and further features of the present invention will becomemore apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a general arrangement of an example of the related art;

FIG. 2 shows a general arrangement of another example of the relatedart;

FIG. 3 shows a general arrangement of one embodiment of the presentinvention;

FIG. 4 shows an operation flowchart at the time of insertion of a tapecassette performed by a tape-running control circuit in the embodimentof the present invention;

FIG. 5 shows an operation flowchart of a process of measuring athickness of a magnetic tape performed by the tape-running controlcircuit in the embodiment of the present invention;

FIG. 6 shows an operation flowchart of a process of obtaining values,which are used for calculating the thickness of the magnetic tape,performed by the tape-running control circuit in the embodiment of thepresent invention;

FIG. 7 shows an operation flowchart of calculating the thickness of themagnetic tape performed by the tape-running control circuit in theembodiment of the present invention;

FIG. 8 illustrates a diameter of a take-up-reel hub and a diameter of atape-wound take-up-reel hub 205 when all the magnetic tape has beenwound on the take-up-reel hub; and

FIG. 9 shows an operation flowchart at a time of recording andreproducing performed by the tape-running control circuit in theembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 3 shows a general arrangement of one embodiment of the presentinvention. In the FIG., the same reference numerals are given to thoseparts the same as the parts shown in FIG. 2, and the description thereofwill be omitted.

In a magnetic recording and reproducing apparatus 200, a tape cassette202 which contains a magnetic tape 201 is loaded at a predeterminedloading position. In the tape cassette 202, loaded at the predeterminedloading position, a supply-reel hub 203 is engaged with a supply reel204, and a take-up-reel hub 205 is engaged with a take-up reel 206. As aresult, when the supply reel 204 rotates, the supply-reel hub 203rotates integrally with the supply reel 204, and, when the take-up reel206 rotates, the take-up-reel hub 205 rotates integrally with thetake-up reel 206.

Either the supply reel 204 or the take-up reel 206 is coupled with areel motor 208 via a swing gear mechanism 207, and one of these reels isrotated selectively in accordance with the rotation of the reel motor208. The swing gear mechanism 207 selects one of these reels, to which arotation driving force of the reel motor 208 is transmitted, inaccordance with a rotation direction (an arrow-A1 direction or anarrow-A2 direction) of the reel motor 208.

For example, when the reel motor 208 rotates in the arrow-A1 direction,the reel motor 208 is engaged with the supply reel 204, and the rotationdriving force of the reel motor 208 is transmitted to the supply reel204. When the reel motor 208 rotates in the arrow-A2 direction, the reelmotor 208 is engaged with the take-up reel 206, and the rotation drivingforce of the reel motor 208 is transmitted to the take-up reel 206. Thesupply reel 204 or the take-up reel 206 is rotated in accordance with arotation speed of the reel motor 208, and running of the magnetic tape201 is controlled.

The reel motor 208 is connected with a reel-motor driving circuit 209,and rotates in accordance with a driving signal from the reel-motordriving circuit 209. The reel-motor driving circuit 209 is connectedwith a tape-running control circuit 210, generates the driving signal inaccordance with a tape-running control signal supplied by thetape-running control circuit 210, and provides the driving signal to thereel motor 208.

A rotation detecting sensor 211 which detects the rotation of the supplyreel 204, a rotation detecting sensor 212 which detects the rotation ofthe take-up reel 206; a cassette-insertion detecting switch 213 whichdetects insertion of the tape cassette 202, and a tape-end detectingsensor 214 which detects a front end and a rear end of the magnetic tape201 are connected to the tape-running control circuit 210. When theinsertion of the tape cassette 202 is detected by the cassette-insertiondetecting switch 213, the tape-running control circuit 210 causes themagnetic tape 201 contained in the tape cassette 202 to run from thefront end to the rear end. At this time, the tape-running controlcircuit 210 measures a thickness of the tape 201, and, also, detects atotal number of revolutions of the take-up reel 206. Then, thetape-running control circuit 210 generates the tape-running controlsignal, for controlling the rotation of the reel motor 208, by using thedetected thickness of the tape 201, the total number or revolutions ofthe take-up reel 206, and a ratio between rotation periods of the supplyreel 204 and the take-up reel 206 when the magnetic tape 201 is running.

Operations of the tape-running control circuit 210 when the tapecassette 202 is inserted into the magnetic recording and reproducingapparatus 200 will now be described.

FIG. 4, shows an operation flowchart performed by the tape-runningcontrol circuit 210 in the embodiment of the present invention.

When the cassette-insertion detecting switch 213 detects that the tapecassette 202 has been loaded at the predetermined loading position (in astep S1-1), the tape-running control circuit 210 sends instructions tothe reel-motor driving circuit 209 for rewinding the magnetic tape 201at high speed (in a step S1-2).

When the tape-running control circuit 210 sends instructions to thereel-motor driving circuit 209 for rewinding the magnetic tape 201 athigh speed in the step S1-2, the reel-motor driving circuit 209 rotatesthe reel motor 208 in the arrow-A1 direction at high speed. As a resultof the reel motor 208 being rotated in the arrow-A1 direction at highspeed, the swing gear mechanism 207 is coupled with the supply reel 204,the supply reel 204 is rotated in an arrow-B1 direction at high speed,and the supply-reel hub 203 of the tape cassette 202 is rotated in thearrow-B1 direction at high speed.

When the supply-reel hub 203 of the tape cassette 202 is rotated in thearrow-B1 direction at high speed, the magnetic tape 201 is wound on thesupply-reel hub 203, and the magnetic tape 201 runs in an arrow-C1direction at high speed. When the magnetic tape 201 has been rewound tothe front end thereof, the tape-end detecting sensor 214 detects thefront end of the magnetic tape 201.

When the tape-end detecting sensor 214 detects the front end of themagnetic tape 201 (in a step S1-3), the tape-running control circuit 210sends instructions to the reel-motor driving circuit 209 for stoppingrunning of the magnetic tape 201 and, thereby, the running of themagnetic tape 201 is stopped (at a step S1-4). At this time, themagnetic tape 201 is not wound on the take-up-reel hub 205.

Then, the tape-running control circuit 210 resets, to zero, a countvalue of rotation pulses supplied by the rotation detecting sensor 211which detects the rotation of the supply reel 204 and a count value ofrotation pulses supplied by the rotation detecting sensor 212 whichdetects the rotation of the take-up reel 206 (in a step S1-5).

After resetting the count values of the rotation pulses of the supplyreel 204 and the take-up reel 206 in the step S1-5, the tape-runningcontrol circuit 210 sends instructions to the reel-motor driving circuit209 for causing the magnetic tape 201 to run at high speed (fastfeeding) (in a step S1-6).

When the tape-running control circuit 210 sends the fast-feedinginstructions to the reel-motor driving circuit 209 in the step S1-6, thereel-motor driving circuit 209 causes the reel motor 208 to rotate inthe arrow-A2 direction at high speed. As a result of the reel motor 208rotating in the arrow-A2 direction at high speed, the swing gearmechanism 207 is coupled with the take-up reel 206 so that the take-upreel 206 rotates in an arrow-D1 direction at high speed, and thetake-up-reel hub 205 of the tape cassette 202 rotates in the arrow-D1direction at high speed.

When the take-up-reel hub 205 of the tape cassette 202 rotates at thearrow-D1 direction at high speed, the magnetic tape 201 is wound on thetake-up-reel hub 205, and the magnetic tape 201 runs in an arrow-C2direction at high speed. At this time, as a result of the magnetic tape201 running in the arrow-C2 direction, the supply reel 204 is rotated inan arrow-B2 direction.

When the take-up reel 206 has rotated a predetermined number ofrevolutions immediately after the magnetic tape 201 starts running inthe arrow-C2 direction, a diameter of the reel hubs (203, 205) ismeasured (in a step S1-7).

The measurement of the diameter of the reel hubs in the step S1-7 willnow be described.

The diameter of the reel hubs (203, 205) is represented by ‘d’ (mm), atheoretically determined thickness (manufacturer's nominal value or thelike) of the magnetic tape 201 is represented by ‘t₀’ (mm), a number ofturns of the tape 201 wound on the supply-reel hub 203 is represented byNs, a number of turns of the tape 201 wound on the take-up-reel hub 205is represented by Nt, a diameter of the tape-wound supply-reel hub 203is represented by øs (mm), and a diameter of the tape-wound take-up-reelhub 205 is represented by øt (mm). Then, the diameter øs of thetape-wound supply-reel hub 203 can be expressed as follows:

øs=d+2·Ns·t ₀ (mm)  (11)

The diameter øt of the tape-wound take-up-reel hub 205 can be expressedas follows:

øt=d+2·Nt·t ₀ (mm)  (12)

When the take-up reel 206 has rotated ‘A’ revolutions (2 revolutions),the number Nt of turns of the tape 201 wound on the take-up-reel hub 205is ‘A’ because the magnetic tape 201 was not wound on the take-up-reelhub 205 in the step S1-4. Therefore, the diameter øt of the tape-woundtake-up-reel hub 205 can be expressed as follows:

øt=d+2·A·t ₀  (13)

On the other hand, the diameter øs of the tape-wound supply-reel hub 203can be expressed as follows:

øs=d+2·Nsa·t ₀  (14)

In the above equation, Nsa represents a number of turns remaining on thesupply-reel hub 203 at this time.

Then, a ratio ka between the diameter øt of the tape-wound take-up-reelhub 205 and the diameter øs of the supply-reel hub 203 can be expressedas follows:

øs/øt=(d+2·Nsa·t ₀)/(d+2·A·t ₀)=ka  (15)

From the above equation (15), the diameter ‘d’ of the reel hubs (203,205) can be expressed as follows:

d=2·t₀·(Nsa−A·ka)/(ka−1)  (16)

The ratio ka(=øs/øt) between the diameter øt of the tape-woundtake-up-reel hub 205 and the diameter øs of the tape-wound supply-reelhub 203 is obtained, as will be described in a step S3-5 shown in FIG.6, as the ratio ka(=Ts/Tt) between the rotation periods.

The number Nsa of turns of the tape 201 remaining on the supply-reel hub203 is obtained, as will be described later, in a process for obtainingan actual thickness ‘t’ of the magnetic tape 201. Specifically, thenumber Nsa of turns of the tape 201 remaining on the supply-reel hub 203is obtained a result of the values obtained from the process describedlater with reference to an operation flowchart shown FIG. 6 beingsubstituted in the equation of a step S4-1 shown in FIG. 7.

With reference to FIG. 4 again, the tape-running control circuit 210calculates the actual thickness ‘t’ of the magnetic tape 201, asfollows:

FIG. 5 shows an operation flowchart of a tape-thickness measuringprocess in the embodiment of the present invention.

In the tape-thickness measuring process, as will be described later, theratio ‘ka’ between the rotation periods Ts and Tt of the supply reel 204and the take-up reel 206 when the take-up reel 206 has rotated thepredetermined number ‘A’ of revolutions, a number ‘z’ of turns of themagnetic tape 201 reduced from the supply-reel hub 203 between the timewhen the take-up reel 206 has rotated the predetermined number ‘A’ ofrevolutions and the time when the take-up reel 206 has rotated apredetermined number (A+x) of revolutions, and a ratio ‘kax’ between therotation periods Ts and Tt of the supply reel 204 and the take-up reel206 when the take-up reel 206 has rotated the predetermined number (A+x)of revolutions are obtained (in a step S2-1). (The term ‘rotationperiod’ means the time required for one revolution of the reel,throughout the present specification.) Then, as will be described later,the actual thickness ‘t’ of the magnetic tape 201 is calculated by usingthe ratio ‘ka’ between the rotation periods Ts and Tt of the supply reel204 and the take-up reel 206 when the take-up reel 206 has rotated thepredetermined number ‘A’ of revolutions, the number ‘z’ of turns of themagnetic tape 201 reduced from the supply-reel hub 203 between the timewhen the take-up reel 206 has rotated the predetermined number ‘A’ ofrevolutions and the time when the take-up reel 206 has rotated thepredetermined number (A+x) of revolutions, and the ratio ‘kax’ betweenthe rotation periods Ts and Tt of the supply reel 204 and the take-upreel 206 when the take-up reel 206 has rotated the predetermined number(A+x) of revolutions, obtained in the step S2-1 (in a step S2-2). Thethus-calculated actual thickness ‘t’ of the magnetic tape 201 is storedas the actual thickness ‘t’ of the magnetic tape 201 contained in theloaded tape cassette 202 (in a step S2-3).

A process, in the step S2-1, for obtaining the ratio ‘ka’ between therotation periods Ts and Tt of the supply reel 204 and the take-up reel206 when the take-up reel 206 has rotated the predetermined number ‘A’of revolutions, the number ‘z’ of turns of the magnetic tape 201 reducedfrom the supply-reel hub 203 between the time when the take-up reel 206has rotated the predetermined number ‘A’ of revolutions and the timewhen the take-up reel 206 has rotated the predetermined number (A+x) ofrevolutions, and the ratio ‘kax’ between the rotation periods Ts and Ttof the supply reel 204 and the take-up reel 206 when the take-up reel206 has rotated the predetermined number (A+x) of revolutions, which arenecessary for calculating the actual thickness ‘t’ of the magnetic tape201, will now be described with reference to FIG. 6.

FIG. 6 shows an operation flowchart of a process for obtaining thevalues needed for calculating the actual thickness ‘t’ of the magnetictape, in the embodiment of the present invention.

From the condition where all the magnetic tape 201 has been rewound onthe supply-reel hub 203, rotation pulses supplied by the rotationdetecting sensor 212 which detects the rotation of the take-up reel 206are counted until the number of revolutions which the take-up reel 206has rotated reaches a predetermined number, that is, ‘A’ (in steps S3-1,S3-2).

Because the rotation detecting sensor 212 generates M rotation pulseseach time when the take-up reel 206 rotates one revolution, the numberof revolutions which the take-up reel 206 has rotated can be obtained asa result of dividing a number Pt of rotation pulses, generated by therotation detecting sensor 212, by M. In the step S3-2, it is determinedwhether the number (Pt/M) of revolutions has reached the predeterminednumber ‘A’ of revolutions.

When the number (Pt/M) of revolutions of the take-up reel 206 hasreached the predetermined number ‘A’ of revolutions, the respectiverotation periods Ts, Tt of the supply reel 204 and the take-up reel 206are detected (in steps S3-3, S3-4). Each rotation period can be obtainedby measuring the time required for generation of the M rotation pulsesfor the respective reel. Then, the ratio ka(=Ts/Tt) between the rotationperiods Ts and Tt of the supply reel 204 and the take-up reel 206 iscalculated (in a step S3-5).

Then, a number Ps of rotation pulses of the supply reel 204 and thenumber Pt of the rotation pulses of the take-up reel 206 are counteduntil the number of revolutions which the take-up reel 206 has rotatedreaches (A+x) (in steps S3-6, S3-7 and S3-8).

When the number of revolutions which the take-up reel 206 has rotatedreaches (A+x) in the step S3-8, the number of revolutions which thesupply reel 204 has rotated after the number of revolutions which thetake-up reel 206 had rotated reached ‘A’ is set in ‘z’ (in a step S3-9).

Then, the rotation periods Ts and Tt of the supply reel 204 and thetake-up reel 206 when the number of revolutions which the take-up reel206 has rotated reaches the predetermined number (A+x) of revolutionsare detected (in steps S3-10, S3-11), and the ratio kax(=Ts/Tt) betweenthe rotation periods Ts and Tt is calculated (in a step S3-12).

Actually, each ratio (ka, kax) between the rotation periods Ts and Tt isobtained as a result of obtaining a ratio between a period of therotation pulses (the interval between a pair of successive rotationpulses) generated by the rotation detecting sensor 211 and a period ofthe rotation pulses generated by the rotation detecting sensor 212.

Thus, the ratio ‘ka’ between the rotation periods Ts and Tt of thesupply reel 204 and the take-up reel 206 when the take-up reel 206 hasrotated the predetermined number ‘A’ of revolutions, the number ‘z’ ofturns of the magnetic tape 201 reduced from the supply-reel hub 203between the time when the take-up reel 206 has rotated the predeterminednumber ‘A’ of revolutions and the time when the take-up reel 206 hasrotated the predetermined number (A+x) of revolutions, and the ratio‘kax’ between the rotation periods Ts and Tt of the supply reel 204 andthe take-up reel 206 when the take-up reel 206 has rotated thepredetermined number (A+x) of revolutions, which are necessary forcalculating the actual thickness ‘t’ of the magnetic tape 201, areobtained.

The process of calculating the actual thickness ‘t’ of the magnetic tape201 in the step S2-2, shown in FIG. 5, will now be described withreference to FIG. 7.

FIG. 7 shows an operation flowchart of the process of calculating theactual thickness ‘t’ of the magnetic tape 201 in the embodiment of thepresent invention.

In the tape thickness calculating process, the ratio ‘ka’ between therotation periods Ts and Tt of the supply reel 204 and the take-up reel206 when the take-up reel 206 has rotated the predetermined number ‘A’of revolutions, the number ‘z’ of turns of the magnetic tape 201 reducedfrom the supply-reel hub 203 between the time when the take-up reel 206has rotated the predetermined number ‘A’ of revolutions and the timewhen the take-up reel 206 has rotated the predetermined number (A+x) ofrevolutions, and the ratio ‘kax’ between the rotation periods Ts and Ttof the supply reel 204 and the take-up reel 206 when the take-up reel206 has rotated the predetermined number (A+x) of revolutions, obtainedin the process shown in FIG. 6, are substituted in the calculatingequation of a step S4-1. Further, the predetermined numbers ‘A’ and ‘x’of revolutions are substituted in the same calculating equation. Thus,the number Nsa of turns of the tape 201 remaining on the supply-reel hub203 when the take-up reel 206 has rotated the predetermined number ‘A’of revolutions is calculated.

Then, the diameter ‘d’ of reel hubs (203, 205), obtained in the stepS1-7, shown in FIG. 4, in accordance with the equation (16), and theratio ‘ka’ between the rotation periods Ts and Tt of the supply reel 204and the take-up reel 206 when the take-up reel 206 has rotated thepredetermined number ‘A’ of revolutions, obtained in the step S3-5,shown in FIG. 6, are substituted in the calculating equation of a stepS4-2. Further, the predetermined number ‘A’ of revolutions and thenumber Nsa obtained in the step S4-1 are substituted in the samecalculating equation. Thus, the actual thickness ‘t’ of the magnetictape 201 is calculated.

Thus, it is possible to easily calculate the actual thickness ‘t’ of themagnetic tape 201 by detecting the rotation of the supply reel 204 andthe rotation of the take-up reel 206 through the rotation detectingsensors 211 and 212.

Again with reference to FIG. 4, even after the actual thickness ‘t’ ofthe magnetic tape 201 is obtained in the step S1-8, the magnetic tape201 continues to be caused to run. Then, when all the magnetic tape 201has been wound on the take-up-reel hub 205, the tape-end detectingsensor 215 detects the rear end of the magnetic tape 201 (in a stepS1-9).

When the rear end of the magnetic tape 201 is detected by the tape-enddetecting sensor 214 in the step S1-9, the running of the magnetic tape201 is stopped, and the count value of the number Pt of the rotationpulses of the take-up reel 206 from the front end to the rear end of themagnetic tape 201 is detected (in a step S1-10). The thus-detected countvalue is divided by M, and the result of the division is stored as thenumber N of turns of the magnetic tape 201 wound on the take-up-reel hub205. Then, the tape-running control circuit 210 provides instructions tothe reel-motor driving circuit 209 for rewinding the magnetic tape 201,and causes the magnetic tape 201 to be rewound (in a step S1-11).

When the magnetic tape 201 has been rewound in the step S1-11, and,then, the front end of the magnetic tape 201 is detected by the tape-enddetecting sensor 214 (in a step S1-12), the running of the magnetic tape201 is stopped (in a step S1-13). Then, a predetermined total tape woundamount S, which will be described later, is calculated from the diameter‘d’ of the reel hubs (203, 205) obtained in the step S1-7, the actualthickness ‘t’ of the magnetic tape 201 obtained in the step S1-8 and thenumber N of turns of the magnetic tape 201 wound on the take-up-reel hub205 obtained in the step S1-10, and is stored (in a step S1-14).

Calculation of the total tape wound amount S will now be described.

FIG. 8 illustrates the diameter ‘d’ of the take-up-reel hub 205 and thediameter ø0 of the tape-wound take-up-reel hub 205 when all the magnetictape 201 has been wound on the take-up-reel hub 205.

When the number of turns of the magnetic tape 201 wound on thetake-up-reel hub 205 is N, that is, when all the magnetic tape 201 hasbeen wound on the take-up-reel hub 205, the diameter ø0 of thetape-wound take-up-reel hub 205 is obtained by the following equation:

ø0=d+2·N·t  (17)

The outer circumferential length 1k of the tape-wound take-up-reel hub205 when the number of turns of the magnetic tape 201 wound on thetake-up-reel hub 205 is k is obtained by the following equation:

1k=π·(d+2·k·t)  (18)

The total length L of the magnetic tape 201 is obtained, from the aboveequation (18), by the following equation: $\begin{matrix}\begin{matrix}{L = {{\sum\limits_{k = 1}^{N}\quad {1k}} = {{{N \cdot \pi}\quad d} + {2\quad {\pi \cdot t}{\sum\limits_{k = 1}^{N}\quad k}}}}} \\{= {{N\quad \left( {{\pi \cdot d} + {\pi \cdot t}} \right)} + {N^{2}\quad {\pi \cdot t}}}}\end{matrix} & (19)\end{matrix}$

The total tape wound amount S is obtained by the following equation byusing the diameter ‘d’ of the reel hubs (203, 205) obtained in the stepS1-8, the actual thickness ‘t’ of the magnetic tape 201 and the totallength L of the magnetic tape 201:

S=t·L+2πd ²/4  (20)

The tape-running control circuit 210 stores the total tape wound amountS calculated by the equation (20), and is used for controlling the reelmotor 208 at the time of data recording or reproducing.

Actually, many values of the total tape wound amount S are previouslycalculated for possible various cases in accordance with theabove-described method, and are stored in a memory. Then, when the tapecassette is loaded, an appropriate one of these many values is read fromthe memory in accordance with the various measured values.

Control of rotation of the reel motor 208 at the time of data recordingor reproducing will now be described.

FIG. 9 shows an operation flowchart at the time of data recording orreproducing in the embodiment of the present invention.

The tape-running control circuit 210 detects the rotation periods of thesupply reel 204 and the take-up reel 206 through the rotation detectingsensor 211 and the rotation detecting sensor 212 (in a step S5-1).

Then, the tape-running control circuit 210 calculates the sum of thesquares of the rotation periods of the supply reel 204 and the take-upreel 206, detected in the step S5-1 (in a step S5-2).

The sum of the squares of the rotation periods Ts and Tt of the supplyreel 204 and the take-up reel 206 is expressed by the followingexpression:

Ts ² +Tt ²  (21)

The sum of the squares of the rotation periods Ts and Tt of the supplyreel 204 and the take-up reel 206 expressed by the expression (21) isconstant, and the constant is expressed by a function of a tape runningspeed Vt and the above-mentioned total tape wound amount S, as follows:

Ts ² +Tt ²=4·π·S/Vt ²  (22)

The right-hand side of the above equation (22) is easily calculated fromthe total tape wound amount S which is calculated when the tape cassette202 is inserted and the constant tape running speed Vt at which themagnetic tape 201 should be caused to run.

As a result of subtracting the theoretical value 4·πS/Vt² at theright-hand side of the above equation (22) from the sum of the squares(Ts²+Tt²) of the rotation periods Ts and Tt of the supply reel 204 andthe take-up reel 206 calculated in the step S5-2, an error signal isobtained (in a step S5-3).

It is possible that many values of this error signal are previouslycalculated for each value of the total tape wound amount S and forvarious values of the rotation periods Ts, Tt, and are stored in amemory. Then, when the tape cassette 202 is inserted, an appropriate oneof the stored values may be read from the memory in accordance with thecalculated total tape wound amount S and detected rotation periods Tsand Tt.

Then, a phase error signal is obtained from a reproduced signal and arotation angle of the rotation drum 7 through a predetermined TT timecalculating process (in a step S5-4). The phase error signal indicates adifference between an angle of the tracks written on the magnetic tape201 and a scanning angle of the heads provided on the rotation drum 7.

A final error signal is obtained as a result of adding the phase errorsignal obtained in the step S5-4 to the error signal obtained in thestep S5-3 (in a step S5-5).

By using the final error signal obtained in the step S5-5, the runningcontrol signal provided to the reel-motor driving circuit 209 iscontrolled (in a step S5-6). That is, the rotation speed of the take-upreel 206 is controlled so that the value of the final error signal willbe zero.

During data recording or reproducing, the steps S5-1 through S5-6 arerepeated (in a step S5-7). Thereby, the constant tape running speed isobtained irrespective of the diameters of the tape-wound reel hubs (203,205).

In the embodiment, when the tape cassette 202 is inserted, rewinding andfast feeding of the magnetic tape 201 are performed, and, thereby, thetotal tape wound amount S is detected. Several minutes are required forthese operations. However, in such a DDS system, several tens of minutesare required for starting up the system when a tape cassette is loaded.Therefore, the fact that several minutes are required for theabove-mentioned operations does not cause any problem.

Further, although the embodiment is the DDS system, a system which thepresent invention can be applied to is not limited to the DDS system.The present invention can be applied to a system such as a DAT in whicha tape is caused to run at a desired speed.

Further, the present invention is not limited to the above-describedembodiment, but variations and modifications may be made withoutdeparting from the scope of the present invention.

The contents of the basic Japanese Patent Application No. 9-346786,filed on Dec. 16, 1997, are hereby incorporated by reference.

What is claimed is:
 1. A tape running control method used in a taperunning apparatus in which a tape runs between a supply reel and atake-up reel, wherein a rotational speed of said take-up reel andtherefore the running speed of said tape are controlled by usingrotation periods of said supply reel and said take-up reel, said methodcomprising the steps of: measuring a thickness of said tape; calculatinga predetermined total tape wound amount by using the detected thicknessof said tape; and controlling the rotation speed of said take-up reel byusing the thus-calculated total tape wound amount.
 2. The tape runningcontrol method as claimed in claim 1, wherein said step of measuring thethickness of said tape comprises the steps of: detecting said rotationperiods of said supply reel and said take-up reel when said take-up reelhas rotated predetermined numbers of revolutions; calculating a numberof turns of said tape remaining on said supply reel by using thethus-detected rotation periods; and calculating the thickness of saidtape by using the thus-calculated number of turns of said tape remainingon said supply reel.
 3. A tape running control method in which a taperuns between a supply-reel and a take-up reel, and a rotation speed ofsaid take-up reel is controlled by using rotations periods of saidsupply reel and said take-up reel, thereby a running speed of said tapebeing controlled, said method comprising the steps of: detecting athickness of said tape, further comprising the steps of: detectingrotation periods of said supply reel and said take-up reel when saidtake-up reel has rotated predetermined numbers of revolutions;calculating a number of turns of said tape remaining on said supply reelby using the thus-detected rotation periods calculating the thickness ofsaid tape by using the thus-calculated number of turns of said taperemaining on said supply reel; calculating a ratio between rotationperiods of said supply reel and said take-up reel detected when saidtake-up reel has rotated a predetermined first number of revolutions;calculating a ratio between rotation periods of said supply reel andsaid take-up reel detected when said take-up reel has rotated apredetermined second number of revolutions; obtaining a differencebetween a number of revolutions which said supply reel has rotated whensaid take-up reel has rotated said predetermined first number ofrevolutions and a number of revolutions which said supply reel hasrotated when said take-up reel has rotated said predetermined secondnumber of revolutions; calculating the number of turns of said taperemaining on said supply reel by using the thus-calculated ratiosbetween the rotation periods and the thus-obtained difference; andcalculating the thickness of said tape by using the thus-calculatednumber of turns of said tape remaining on said supply reel; andcalculating a predetermined total tape wound amount by using thedetected thickness of said tape; and controlling the rotation speed ofsaid take-up reel by using the thus-calculated total tape wound amount.